Moyes is perfect for MU. I dont see any other manager capable of replacing SAF
Klopp? He would stay at Dortmund. The only way for him to leave Dortmund is if someone at Germany (like Munchen or the national team) offering a job there
Mourinho? He's going to Chelsea
Heynckess? He would retire for maybe a year or get job elsewhere but for sure he wont go to Premier league next year (he never had interest there)
so who else is capable of replacing SAF?
it's also a bit unfair to look at head to head comparison between Everton and the other big clubs. Everton WAS a very small club before Moyes came there and he made it a team capable of fighting the 4th-7th spot every year. That's one good consistency there. You can't compare him with Fergie because Fergie always managed to hold his stars back in 90s while Moyes live in globalization era where his stars (like Rooney in the past and now Feilani and Baines) are always being chased by other big clubs not to mention competition in Premier League is quite fierce with that Russian and arab moneys for City/Chelsea.
Point is, during the first 6-8 years of Fergie reigns, he had less competition and less offers for his star players hence why he could keep his stars. Moyes' reign in Everton was pretty much different. Moyes faced fierce competition from big budget clubs and his players often receive temptations to play in other clubs yet he could bring Everton to 4th-8th every year. Im not a big fan of Moyes but honestly he's underrated.
I even think he's way better than Wenger and Benitez. That doesnt mean he will be automatically capable of managing MU though. It's a very different matter. It reminds me to AVB whom succeeded massively with Porto but failed miserably with Chelsea. A lot of managers who succeeded in mid tier clubs failed when they got promoted (AVB, Pellegrini, etc.) so who knows if Moyes would be just another one. There are doubts but time will tell